Vishishtadvaita is inseparable from Sri Vaishnavism, the South Indian devotional tradition Ramanuja inherited and gave philosophical form. The school calls its own method ubhaya vedanta, the twin Vedanta, because it treats the Sanskrit Upanishads and Brahma Sutras as one authoritative source and the Tamil devotional hymns of the Alvar poet-saints, collected as the Divya Prabandham, as a second, equally canonical source of the same truth, sung rather than reasoned. Ramanuja's own teaching accordingly runs on two registers at once, a rigorous scholastic philosophy defending the reality of a qualified, differentiated Brahman against Advaita, and a warm devotional theology in which Vishnu, worshipped as Narayana together with his consort Sri, is approached through prapatti, total surrender, as much as through philosophical understanding.
The school's doctrine of grace follows directly from its metaphysics. Because souls are real, dependent parts of God rather than illusory appearances destined to dissolve, their relationship to God is genuinely personal and can genuinely be marked by love, dependence and rescue rather than by the dispassionate self-knowledge Advaita prescribes. Later Sri Vaishnava teachers debated exactly how much the soul must do to secure that grace, a question later schools within the tradition answered differently, but the underlying vishishtadvaita metaphysics, one reality, really differentiated, really related as body to self, remained the fixed philosophical foundation beneath every version of that debate.